Washington: Britain will on Tuesday mark 10 years since the London bombings with a minute`s silence for the 52 victims, less than a fortnight after an attack in Tunisia highlighted the ongoing Islamist threat.

Thirty Britons were among 38 people killed when a gunman went on the rampage at a popular Tunisian beach resort on June 26, Britain`s worst terror incident since four suicide bombers attacked the London transport network on July 7, 2005.

"Ten years on from the 7/7 London attacks, the threat from terrorism continues to be as real as it is deadly," Prime Minister David Cameron said.

"The murder of 30 innocent Britons whilst holidaying in Tunisia is a brutal reminder of that fact. But we will never be cowed by terrorism."

In the past decade, successive governments have strengthened security powers and improved the way the emergency services respond to attacks.

But they are still struggling to address the problem of radicalisation exposed by the bombings, which were carried out not by foreign fighters but by four young men from Yorkshire in northern England who were inspired by al Qaeda.

Hundreds of British young people are now flocking to join the Islamic State group in Syria and Iraq, raising fears that they might return to attack their homeland.

"We will keep on doing all that we can to keep the British public safe, protecting vulnerable young minds from others` extremist beliefs and promoting the shared values of tolerance, love and respect that make Britain so great," Cameron said.

The commemorations begin with a wreath-laying at the national memorial in Hyde Park at 8:50 am (0750 GMT), marking the moment the first three bombs exploded on London Underground trains at Aldgate, Edgware Road and Russell Square stations.

An hour later, a fourth suicide bomber blew himself up on a double-decker bus in Tavistock Square near Russell Square, killing and injuring some of those who had been evacuated from the Underground.Relatives and survivors will gather at the Hyde Park memorial later in the day to lay flowers, while there will also be a service at St Paul`s Cathedral.

A nationwide minute`s silence will be held at 1030 GMT, the second such gesture in four days after Britain fell silent on Friday for those killed in Tunisia.

For many of those directly affected by the London bombings, the anniversary has brought back painful memories.

David Boyce was a 25-year-old supervisor at Russell Square station and one of the first to witness the carnage.

"There was body parts all over the place and dead bodies lying all over the train," he told AFP in an interview.

He added: "The first person I came across, both his legs had got blown off.

"So using my own clothes I made a tourniquet, lifting his legs above his heart, made him more comfortable, let him know that help was on the way."

Many lives were saved by people such as Boyce, but the general emergency response was fractured, hampered by poor communications inside the tunnels and between controllers.

This has been overhauled, as has the government`s counter-terrorism strategy, with new measures introduced to clamp down on radical preachers and give police and security services tougher powers to question and track suspects.

This year Cameron`s government also moved to seize passports from Britons going to fight with the IS group, and it is working on highly controversial plans to increase the collection of mobile phone and Internet data.

The national terror threat remains severe, the second highest of five levels meaning an attack is highly likely.